Abstract

Bacillus megaterium SW1-2 producing polyhydroxalkanoate (PHA), previously isolated from activated sewage sludge was selected for the study of polyhydroxybutyrate (PHB) biopolymer production. Preliminary experiment showed that the strain capable of producing 36% cell dry weight (CDW) of the polymer during growth on basal E2 medium supplemented with glucose, followed by 28, 15 and 8% CDW during growth on Na-acetate, lactose or Na-succinate, respectively. Spectroscopic analysis by FT-IR revealed characteristic peaks at 1722.8 and 1276 cm^-1 corresponding to the C=O and C-O stretching groups indicated that the polymer composed mainly of polyhydroxybutyrate (PHB). Statistically based experiments were applied to optimize the culture conditions for production of PHB. Four selected parameters namely; ammonium sulfate, glucose, KH₂PO₄ and Na₂HPO₄, respectively, were further investigated using Box-Behnken design to define the optimal production condition. Based on statistical analysis, maximal PHB production (1.45 g/l) was reached using optimal medium composition, which is more than 1.8-folds the basal medium. Verification experiment was carried out to examine model validation and revealed more than 75% validity.

Key words: Polyhydroxybutyrate, Bacillus megaterium, Box-Behnken design, optimization.